5 Open Policy Agent Alternatives for Superior Authorization

In today's complex application landscape, authorization is a critical component of security architecture. As developers build increasingly sophisticated systems, they need robust, flexible authorization solutions that can grow with their applications. Open Policy Agent (OPA) has emerged as a popular choice for implementing authorization, but it might not be the best fit for your specific needs.

This article explores five alternatives to Open Policy Agent that offer compelling features for different authorization requirements. We'll examine what makes each solution unique and help you determine which might be the right choice for you.

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Understanding Open Policy Agent and Its Limitations

Before diving into alternatives, let's establish what Open Policy Agent is, the use cases where it shines, and where it might fall short for certain applications.

Open Policy Agent is an open-source, general-purpose policy engine that provides unified policy enforcement across the stack. It uses a high-level declarative language called Rego for policy definition and can be deployed as a sidecar, host-level daemon, or library. In general, teams use Open Policy Agent to enforce policy within cloud infrastructure.

While OPA offers flexibility as a general-purpose policy engine, this broad focus comes with tradeoffs:

• The Rego language has a significant learning curve
• As a general-purpose tool, it lacks application-specific authorization primitives
• Implementation requires substantial custom integration work
• Performance can be a concern in high-throughput scenarios

These limitations have led many development teams to seek alternatives that better align with their specific authorization needs.

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Alternative 1: Oso

Oso takes a fundamentally different approach to authorization by focusing specifically on application authorization rather than being a general-purpose policy engine. This specialized focus translates to practical advantages for development teams.

Key Differentiators:

• Purpose-built for application authorization: Unlike OPA's general-purpose approach, Oso’s policy language, Polar, provides primitives specifically designed for application authorization patterns[1]
• High-performance data model: Oso’s data model is optimized for authorization operations. Oso can even work directly with your application data when you need to squeeze every last bit of performance out of larger operations like filtering lists.
• Developer-friendly implementation: The authorization logic can mirror your application code, reducing the complexity of implementation

Oso's specialized focus makes it particularly well-suited for teams that need to implement application authorization models like role-based access control (RBAC), attribute-based access control (ABAC), or relationship-based access control (ReBAC) without the overhead of a general-purpose policy engine.

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Alternative 2: AWS Cedar

AWS Cedar represents another specialized approach to authorization, with a focus on readability and application-level authorization.

Key Differentiators:

• Readability focus: Cedar's policy language prioritizes human readability and understanding while also providing a syntax that resembles AWS IAM definitions. It occupies a middle ground between Rego and Polar.
• Structured design: Cedar offers a more structured approach to policy definition compared to OPA's Rego
• Application-level authorization: Like Oso, Cedar focuses specifically on application authorization rather than general policy enforcement

Cedar's safety-oriented approach and fine-grained permissions make it a strong contender, particularly for applications on AWS. However, it has limited tooling and smaller community support compared to more established alternatives.

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Alternative 3: Google Zanzibar Based Tools

For applications that need to manage complex relationship-based permissions at scale, tools like AuthZed or Auth0, which are based on Google Zanzibar, offer a compelling alternative to OPA.

Key Differentiators:

• Graph-based authorization model: Zanzibar clones excel at managing access control via relationships
• Single source of truth: Systems based on Zanzibar centralize the source of authorization decisions
• Relationship-focused: Particularly strong for applications where permissions depend on complex relationships between users and resources

While Zanzibar offers powerful capabilities for relationship-based authorization, it introduces system complexity by requiring centralization of all authorization data. As a result, you will need to store, copy, and sync data across your application and your authorization service. It also forces you to model your authorization logic as relationships, which makes it challenging to implement ABAC.

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Alternative 4: XACML

The eXtensible Access Control Markup Language (XACML) represents a standards-based approach to authorization that predates OPA and other newer alternatives.

Key Differentiators:

• Standardized approach: As an OASIS standard, XACML offers a well-defined, standardized framework
• Mature ecosystem: With a longer history, XACML has established patterns and implementations
• Comprehensive model: Includes a complete policy language, architecture, and request/response protocol

However, XACML's XML-based approach can be verbose and complex compared to newer alternatives, and it may not be as well-suited for modern cloud-native applications as some of the other options discussed here[2].

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Alternative 5: Hashicorp Sentinel

Rounding out our alternatives is Hashicorp Sentinel, which takes yet another approach to policy as code.

Key Differentiators:

• Infrastructure focus: Particularly strong for infrastructure-related authorization decisions
• Hashicorp ecosystem integration: Works seamlessly with other Hashicorp products
• Embedded policy engine: Designed to be embedded within other Hashicorp applications and services

Sentinel's focus on infrastructure makes it particularly valuable for teams that need to enforce policies across Hashicorp-based infrastructure as code deployments. It’s not suited for application authorization.[3].

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Choosing the Right Authorization Solution

When evaluating these alternatives to Open Policy Agent, consider these key factors:

• Use case: Are you looking for infrastructure or application authorization?
• Integration complexity: How much custom work will be required to implement the solution?
• Performance requirements: Can the solution meet your latency and throughput needs?
• Team expertise: Which solution aligns best with your team's existing knowledge and skills?
• Deployment model: Does the solution support your required deployment scenarios?

The right choice depends heavily on your specific requirements. For teams building complex applications with sophisticated authorization needs, purpose-built solutions like Oso often provide advantages over general-purpose policy engines like OPA.

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Comparing Key Features

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Implementation Considerations

Before implementing any authorization solution, consider these questions:

• How easy is it to get started? Is it a cloud service or do you have to deploy it to your infrastructure?
• How much support does it require? Do you have the capacity and infrastructure to provide it?
• What’s the developer experience like? Is it easy to onboard new developers and integrate with your existing development process?
• How is the documentation? Can you quickly find the information you need?
• Does the solution support your authorization needs? Will it support them in 6 months? A year? Beyond?
• Will the solution meet your current performance requirements? Will it continue to do so as your application grows?

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Conclusion

While Open Policy Agent offers a flexible, general-purpose approach to policy enforcement, purpose-built alternatives often provide advantages for specific authorization scenarios. By understanding the strengths and limitations of each option, you can select the solution that best fits your unique requirements.

For teams building complex applications with sophisticated authorization needs, solutions like Oso that focus specifically on application authorization often provide the best balance of power, flexibility, and developer experience. The right choice ultimately depends on your specific requirements, existing technology stack, and team expertise.
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Citations

[1] https://www.osohq.com/post/oso-vs-opa-open-policy-agent-alternatives

[2] https://www.styra.com/blog/opa-vs-xacml-which-is-better-for-authorization/

[3] https://www.jit.io/resources/security-standards/5-use-cases-for-using-open-policy-agent